1. Field of the Invention
The present invention relates to a pressed-contact type semiconductor device, such as a thyristor, GTO (Gate Turn-off) thyristor, GCT (Gate Commutated Turn-off) thyristor or the like, which has reverse-blocking capability required for applying a circuit in an industry or power control system.
2. Description of the Related Art
In the conventional pressed-contact type semiconductor device, a P++-type semiconductor layer is formed by diffusing P-type impurities on a front side of an N−-type semiconductor substrate, a P-type semiconductor layer is formed by diffusing P-type impurities on the back side of the semiconductor substrate, and an N-type semiconductor layer having a depth shallower than that of the P++-type semiconductor layer is formed by diffusing N-type impurities on the front side of the semiconductor substrate. Thus, there is provided a PNPN-junction structure as the whole, allowing thyristor operation.
The related prior arts are listed as follows: Japanese Patent Unexamined Publications (koukai) JP-A-8-264754 (1996), JP-A-9-260640 (1997), JP-A-3-120724 (1991) and JP-A-8-116047 (1996).
According to a reverse-blocking type GCT thyristor developed from a thyristor, the higher an operation frequency of the device becomes, the more a ratio occupied by switching loss is increased in the whole generated loss. Therefore, it has been desired to optimize turn-off loss and reverse recovery loss.